<html>
<head>
    <title>a - test</title>
</head>
<body>
<h1>page a</h1>
<div>a</div>
</body>
<script>
    setTimeout(() => {
      let el = document.createElement('div');

      el.dataset.name = 'el';
      el.innerHTML = 'content';

      document.body.appendChild(el)
    }, 500)
</script>
</html>
